It is generally known to provide a crane having at least one crane girder, such as a trussed girder, that extends horizontally and has an upper run and a lower run, with a crane trolley having a lifting gear being movably mounted thereto. However, the conventional production of crane girders involves beginning with components at an excess size, followed by subsequent burning off or shortening the components to the desired finished size or length.
For example, German patent specification DE 260 030 discloses a so-called double-girder gantry crane having two horizontal crane girders and two vertical support girders that form a gantry frame of the gantry crane. The crane girders extend in parallel and at a spaced interval with respect to each other. Arranged at each of the lower ends of the support girders is a travelling mechanism, by means of which the gantry crane can be moved in a direction of travel extending transversely with respect to the longitudinal direction of the crane girders. A crane trolley having a cable winch can be moved on and along the crane girders. According to the design as a double-girder crane, a load picking-up means of the cable winch arranged on the crane trolley is lowered or raised between the two crane girders. The crane girders are formed as a trussed girder and include in each case an upper run and a lower run which are each oriented horizontally and in parallel with each other. The upper and lower runs of the two crane girders are connected to one another by means of vertically extending, rod-shaped posts and diagonally extending, rod-shaped struts. The two crane girders are connected to one another at their ends by means of transverse rods and struts to form a frame. Rod-shaped posts and struts are provided along the longitudinal direction of the crane girders between the upper and lower run as a type of truss and each connect an upper run to the lower run arranged vertically therebelow.
German utility model document DE 1 971 794 U describes a double-girder overhead crane whose two horizontal crane girders are connected to one another by means of head girders arranged at the respective ends thereof and can be moved together in a direction of travel extending transversely with respect to the longitudinal direction of the crane girders. Both crane girders are designed in a similar manner as trussed girders and include in each case plate-shaped upper runs, rod-shaped lower runs and rod-shaped posts.
German patent specification DE 31 09 834 C2 relates to a tower crane having a mast and a crane jib that are formed as trussed structures. The cuboidal mast includes four L-shaped and vertically oriented support girders, of which two adjacent support girders are each connected to one another by means of triangular plates. In this case, the plates are attached with their corner regions and/or one of their sides to the support girders. At least some of the sides of the plates are folded and form stiffening ribs.
Furthermore, German utility model DE 1 971 793 U1 discloses a crane girder of an overhead crane that is designed as a box girder. At its two opposite ends, the crane girder is screwed in each case to a head girder by means of connecting elements. The head girders support travelling mechanisms, with which the overhead crane can be moved along rails. The connecting plates are made up of a rectangular base plate, on which two rectangular fastening plates are welded in each case in an inwardly offset manner. The fastening plates are each positioned perpendicularly on the base plate and are arranged in parallel and at a spaced interval with respect to one another corresponding approximately to the width of the crane girder. Therefore, the connecting elements can be slid with their fastening plates over the ends of the crane girders, oriented and welded in the desired position.